The present invention generally relates to a moving bed ion exchange apparatus and method, especially one incorporating folded resin flows to significantly reduce the height of the apparatus and thus decrease the amount of head space required. More particularly, this invention achieves folded features in a countercurrent system having the ability to accomplish an in-phase and a laminar flow of ion exchange resin during the transfer thereof in a moving bed arrangement. Countercurrent flow of the regeneration and rinsing solutions is practiced while maintaining a packed bed condition even though the system retains the advantages of a moving bed.
Moving bed ion exchange systems are known to have several advantages, especially improved efficiency, over fixed bed systems. Units such as in Higgins U.S. Pat. No. 2,815,322 and Keller U.S. Pat. No. 3,325,011 have a closed loop which incorporates a treating zone through which the liquid to be treated is passed in order to effect an ion exchange, as well as a regeneration zone wherein a regenerating solution is passed through the resin. Between successive service cycles of these systems, the resin is advanced through the closed loop for providing regenerated resin within the treating zone. Keller, for example, shows a treating zone directly above a regeneration zone, and the resin supply is pumped by compressed air to advance from the regeneration zone to the treating zone to force used resin out of the treating zone and to the pumping location. Units such as Yomiyama U.S. Pat. Nos. 3,152,072; Mihara 3,238,125; and Yamashiki 3,378,339, have multiple resin vessels and show resin movement therebetween. They cause feed liquid to flow upwardly which, upon initiation of fluid flow after resin transfer, causes the resin bed to turbulate with great mixing of partially loaded resin with newly regenerated resin and consequent loss in stage transfer heights and cutting of resin regeneration capacity.
While such systems have advantages over fixed-bed systems because regenerated resin is continuously supplied, even those having multiple resin beds have the disadvantages of a loose bed, including development of an out of phase condition, non-laminar movement, and undesirable bed expansion.
The present invention retains the general advantages of moving-bed systems while avoiding the disadvantages of previously known moving-bed systems due to the ability of the present system to incorporate desirable packed-bed attributes into a moving-bed system at all times. In the present invention, when moving the ion exchange resin through and between the various vessels or columns, the liquid-to-resin relationship remains in phase; that is, the liquid does not go faster than the resin so that the interfaces stay intact and at a constant relationship to each other, which brings about a final result of improved ion exchange such that it approaches stoichiometric ratios and such that no excess rinse is required to move the resin interfaces back to their various operational positions. By the present invention, the resin bed is in a packed condition at all treatment times.
In another aspect of this invention, the present system unlike prior art systems does not move the entire resin inventory during the resin transfer, which total movement results in extensive mixing of resin and fluid causing fluid slippage in the direction of resin movement, whereby the liquid moves faster than the bed so that the liquid and the ion exchange resin material are not in contact with each other for a sufficient period of time in order to achieve the desired result, whether that result be an ion exchange or the removal of entrained liquids. When a unit exhibiting fluid slippage goes back on stream after having been shut down for a significant period of time, the chemical efficiency of the unit is lost until the bed repacks itself and re-establishes equilibrium conditions, which could take as long as twenty percent of the time required to complete an entire closed loop cycle for short cycles of several minutes.
Another aspect of this invention brings with it an advantageous "stage height" feature which approximates the functional operation of a fractionating tower whereby, for example, in the regeneration vessel or column, the purest resin is in contact with the purest regeneration fluid; and, as the resin becomes more contaminated in the lower portions of that column, the regenerating liquid likewise becomes correspondingly more contaminated, with the most contaminated regenerating fluid within the regeneration reservoir being in contact with the spent ion exchange resin just received from the treating or loading vessel. Such a stage height feature provides the maximum equilibrium or mass flow kinetic effect possible in such a system.
A still further aspect of this invention is the fact that the various passageways or distributors of the moving resin bed have a very simple construction and may enhance fluid distribution across the resin bed to eliminate channelling. In prior art systems, large hydraulic forces are developed, requiring massive reinforced distributors which caused obstructions to resin flow or requiring a multiplicity of various small distributors at the bottom of the loading vessel, often to the point that the cross-section was almost entirely screened, which developed points of resin stagnation and resistance to resin flow, thereby inhibiting smooth flow distribution in the vicinity of the fluid discharge in the resin bed. These disadvantages are avoided with the present invention by its in-phase and laminar packed bed condition resin movement.
Another problem with previously known moving-bed systems is the need to accomplish additional start up operations after the system has been idle for relatively long periods of time, such as for several weeks. When such previously known systems were left standing idle for long periods of time, the resin would first have to be transferred manually in order to loosen up the resin packed around and obstructing the operation of the valves, this manual operation usually having to be followed by running the system through several cycles in order to place the system into proper startup condition before actually proceeding with the ion exchange operation on the liquid to be treated. Some systems incorporate a pulsing circuit to move resin while off stream. In accordance with the present invention, the system, even after having been idle for several weeks and without a pulsing circuit, can be immediately started up anywhere within the total program cycle without having to manually transfer any resin or run through start-up cycles.
By yet a further aspect of this invention, two complete units thereof are coupled together in an appropriate manner whereby there can be accomplished the processing of water containing either undesirable substances for removal and disposal or desirable substances for recovery and further processing of same to some beneficial use, together with the additional benefit of deionizing the treated water.
It is, therefore, a general object of the present invention to provide an improved apparatus and method for conducting ion exchange operations through a moving resin bed.
Another object of the present invention is an improved method and apparatus which accomplishes an in phase and laminar flow of resin throughout the system while maintaining countercurrent flow, especially to the extent that the resin interfaces throughout the system are maintained intact and in a packed-bed condition.
Another object of the present invention is to provide an improved moving-bed ion exchange resin system which proceeds through sequential steps during which the liquid being treated moves in a downflow manner, with the upper or initial portion of the loading vessel resin bed being removed therefrom for subsequent regeneration, rinsing, and reuse.
Another object of this invention is to provide a system suitable for either removing contaminants such as for water softening, or recovering valuable material such as precious metals from a liquid to be treated, even when only trace amounts of those contaminants or valuable materials are present in the liquid.
Another object of the present invention is to provide a method and apparatus for removing and recovering copper, lead, nickel and the like from the rinse water of a printed circuit manufacturing operation, to the extent that the rinse water is purified so that it is characterized as deionized water which can be recycled for use in the printed circuit manufacturing process itself.
Another object of this invention is to provide a moving-bed resin system wherein a laminar flow is maintained throughout the system whereby the interfaces of the resin remain intact during their flow throughout the system.
Another object of the present invention is to provide an improved ion exchange resin system which is of the moving-bed type affording sequentially continuous operation but which is and has the advantages of a packed bed system.
Another object of this invention is an improved apparatus and method having a "stage height" feature similar in end results to that of a fractionating tower whereby the purest resin is in contact with the purest regenerating fluid and progressively more contaminated resin is correspondingly in contact with progressively more contaminated regenerating fluid.